Why be good?

[Wyrd of Gawd]

Your description of hell as separation from god (despite mentions of hellfire) in various places.  

Before I forget...there is nothing "extra-biblical" about Purgatory...there are lots of verses that refer to Purgatory - though the word itself (like "trinity") does not appear.

But as for your request, here is one passage:

Matthew 25
31 “When the Son of man comes in his glory, and all the angels with him, then he will sit on his glorious throne. 32 Before him will be gathered all the nations, and he will separate them one from another as a shepherd separates the sheep from the goats, 33 and he will place the sheep at his right hand, but the goats at the left. 34 Then the King will say to those at his right hand, ‘Come, O blessed of my Father, inherit the kingdom prepared for you from the foundation of the world; 35 for I was hungry and you gave me food, I was thirsty and you gave me drink, I was a stranger and you welcomed me, 36 I was naked and you clothed me, I was sick and you visited me, I was in prison and you came to me.’ 37 Then the righteous will answer him, ‘Lord, when did we see thee hungry and feed thee, or thirsty and give thee drink? 38 And when did we see thee a stranger and welcome thee, or naked and clothe thee? 39 And when did we see thee sick or in prison and visit thee?’ 40 And the King will answer them, ‘Truly, I say to you, as you did it to one of the least of these my brethren, you did it to me.’ 41 Then he will say to those at his left hand, ‘Depart from me, you cursed, into the eternal fire prepared for the devil and his angels; 42 for I was hungry and you gave me no food, I was thirsty and you gave me no drink, 43 I was a stranger and you did not welcome me, naked and you did not clothe me, sick and in prison and you did not visit me.’44 Then they also will answer, ‘Lord, when did we see thee hungry or thirsty or a stranger or naked or sick or in prison, and did not minister to thee?’ 45 Then he will answer them, ‘Truly, I say to you, as you did it not to one of the least of these, you did it not to me.’ 46 And they will go away into eternal punishment, but the righteous into eternal life.”

That passage from Matthew chapter 25 is basic Zoroastrian philosophy as is all of the passages that discuss righteousness and angels.  Christianity incorporates a lot of Zoroastrian doctrine, especially the ideas of the savior and the trinity.